This invention relates to a head-mounted projection display system, and more particularly relates to such a display system in which the display is stereoscopic.
A variety of head-mounted displays are in use or have been proposed. Usually they involve a CRT or a spatial light modulator coupled to a source of light to create the display image. In the simplest versions, the images are viewed directly by the eye, assisted by suitable optics. See, for example, Japanese Kokai 4-34588 (A). Some versions permit the ambient environment to be viewed through the apparatus while information is added to the observer""s view from the display. See, for example, U.S. Pat. No. 5,677,795.
In UK patent application GB 2 043 940 A, a ground-based craft-flight simulator is described, in which separate right and left light beams from a laser-scanning image generator are fed to right and left projection lenses mounted on a helmet above the eyes of a wearer-trainee, and projected onto a retro-reflective viewing screen. A diffraction grating on the front of the screen adjusts the angle of the retro-reflected image, so that the projected beams are reflected onto a plane mirror mounted on the helmet between the projection lenses and the eyes of the viewer. Motors mounted on the helment rotate the mirror, to achieve scanning of the reflected light beams onto the screen to build up the display image.
As will be appreciated, this system is complex and would be expensive to implement, limiting its applicability to specialized uses such as military or commercial pilot training.
A simple low-power, head-mounted projection display system, particularly one which provides stereoscopic viewing, would be useful in a variety of applications, notably virtual reality systems, useful, for example, in education, training, and/or entertainment.
Accordingly, it is an object of the invention to provide a simple, low-power, head-mounted projection display system.
It is another object of the invention to provide such a head-mounted projection display system in which stereoscopic viewing is possible.
In accordance with one aspect of the invention, there is provided a head-mounted projection display system comprising head gear including at least one low-power projector positioned such that the images from the projector are directed away from the viewer""s eyes. More specifically, the projector is mounted so as to project an image in a direction along the viewer""s line-of-sight. Preferably, a pair of projectors are mounted on opposite sides of the head gear, adjacent the viewer""s eyes, and each projector is aimed to project an image in a direction along the viewer""s line-of-sight.
The projected image is directed to a high-gain, retro-reflective viewing screen, which returns light from the low power projector(s) at sufficient brightness for the viewer to see the projected image(s). Due to the small angle of return (on the order of about 1-2 degrees), each eye sees only the image from its adjacent projector, enabling stereoscopic viewing in the event that separate images are projected by each projector, without the attenuation, temporal or optical manipulation common to known stereoscopic display systems.
The retro-reflective viewing screen is capable of having a wide viewing angle. This characteristic, together with the retro-reflectivity of the screen, permits a single viewer or multiple viewers, each with their own headgear, to see the same image or different images at large angles of view without significant degradation, making possible, for example, one or more viewers moving within the viewing space, or an audience of stationary viewers.